Year 12 : Visual Basic Tutorial.

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1 Year 12 : Visual Basic Tutorial. STUDY THIS Input and Output (Text Boxes) The three stages of a computer process Input Processing Output Data is usually input using TextBoxes. [1] Create a new Windows Application Project called Calculator. Set the Form properties: Property Value Name frmcalculator BackColor Linen Text Calculator Size 350,180 StartPosition CentreScreen [2] Place a TextBox on the form with the following properties: Property Value Name txtfirstnumber Location 30,45 Size 67,20 And a Label with the properties: Property Value Name lblfirst Location 27,29 Text Please enter the first number: Your form should look like this.

2 [3] Add another TextBox (txtsecondnumber) and Label (lblsecond) to the form and line them up so the form looks like : (NOTICE the lines on the form that help you line objects up) [4] Add another TextBox (txtanswer), a Label (lblanswer) and a Button (btnanswer) to your form Arrange your objects to look similar to this diagram. This is the end of the first stage of your program - Creating the interface by adding objects to your form and setting the properties. [5] Stage 2 Adding the code for the event handlers. Only one event-handler to write. The Click event of the Button btnanswer. Double-click on btnanswer to open the Code Window and type this subroutine. Private Sub btnanswer_click 'Declare the variables Dim First As Integer Dim Second As Integer 'Assign values to the variables from the Inputs First = txtfirstnumber.text Second = txtsecondnumber.text 'Output the answer txtanswer.text = First + Second

3 STUDY THIS Explanation: [a] The Green lines are comments. These are important! They explain what each section of code does. These are a useful reminders for YOU and should always be included. Also useful is white space the blank lines between sections of the code. [b] Variables are quantities that may be different each time a program is run. The computer needs to know what variables you are going to use and what type they are. (see List at the end of this section) Your subroutine uses two variables called First and Second. They are both of integer type. [c] First = txtfirstnumber.text The input line. This line assigns the value of the Text property of txtfirstnumber to the variable First. In other words the value of First becomes the number in the Textbox at the time the button is clicked. Make sure you fully understand how an assignment statement works you will be using them a lot! A = B.assigns the value of B to the variable A. This means that the value of A changes but the value of B does not. [d] txtanswer.text = First + Second The output line - txtanswer will display the result of the calculation. This is really another assignment statement, where the value of the Text property of txtanswer is given the value that is the sum of the two numbers. Phew! Some important stuff there! [6] Run the program and check that it works. (Input two numbers and click the button)

4 Table of Data Types. STUDY THIS Data Type Comment Size Example Char Any character 1 byte A String Up to about 2 billion characters 2 bytes per character Tom Jenkins Byte 0 to byte 29 SByte -128 to byte -3 Short -32,768 to 32,767 2 bytes 3278 UShort 0 to 65,535 2 bytes Integer -2,147,483, to 4 bytes 629,439 2,147,483,647 UInteger 0 to 4,294,967,295 4 bytes 3,120,000,000 Long Massive whole 8 bytes 7,444,555,666,777 numbers ULong Massive whole 8 bytes 32,456,457,645,999 numbers Single Real numbers 4 bytes Double Real numbers 8 bytes Decimal Real Numbers 16 bytes 36, Boolean True or False 1 bit True Date Jan 1 st, 0001 to Dec 31 st, bytes 6/3/2012 When a variable is declared in a program, it is really an instruction to the computer to reserve some space in memory, where the value of that variable will be stored. The amount of memory space reserved depends on the type of the variable. (see above table) so it is good programming practice to declare variables as small types whenever possible. Example - Don t use an Integer when a Byte would do. When a subroutine has run and finished, the space reserved for local variables declared in that subroutine will be released.

5 Visual Basic Challenges 1 [1] Create an application that has a Label and two buttons. When one of the buttons is clicked, the message reads Hello in Green, and when the other button is clicked the message reads Goodbye in Red. [2] Create an application where a button displays the message Hello World in RED when the mouse button is pressed down, and in GREEN when the button is released. (HINT : Use The MouseDown and MouseUp events) [3] Create an application which looks like this when run There is an invisible Label below the button. When the program is run, the user enters a name into the TextBox and clicks on the button to reveal the message HINT : You can add text strings together BULL + FROG is the string BULLFROG

6 Other Methods of Input and Output (InputBox; MsgBox) Another method of input involves using an InputBox. [1] You are going to write a program that allows the user to input a number, and outputs its square (Eg Input :7 and output:49) Create an application with a form that has a Button (btndisplay) and a TextBox (txtmessage). Arrange the objects to look like this Enter the following event handler for the Click event of btndisplay Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 'Declare variables Dim Num As Integer Dim Answer As String 'Open the Input Box and assign the value of Num Num = InputBox("Please Enter Your Number", "Input Window") Answer = "The square of " + Num.ToString + " is " + _ (Num * Num).ToString 'Display the message in the TextBox txtmessage.text = Answer The InputBox statement in your subroutine has two parameters both are strings. The first string ( Please Enter Your Number ) is the message prompt, the second ( Input Window ) is the Window title. When the program is run, whatever is typed into the InputBox is returned as the value of variable Num and this variable can then be used in your program. [2] Run the program...and type in your number

7 When you click the OK button, the message should appear in your form. NOTE : Strings may be added together, but sometimes you need to turn a number into a string first. That is why you will see Num.ToString in the message Also If a line of code is too long, place a <space> and a _ character at the end of the line _ and continue on the next. (like the line above) Using an MsgBox. Another way to output data. [1] Create a new application and place a Button (btnoutput) on the Form. Type in the event handler for the Click event of btnoutput Private Sub btnoutput_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles btnoutput.click MsgBox("Keep Smiling!") Run the program. [2] Try changing the subroutine to Private Sub btnoutput_click(byval sender As System.Object, ByVal e As System.EventArgs) Handles btnoutput.click MsgBox("Are you still smiling?", MsgBoxStyle.Question, "Output Demo")